1. Field of the Invention
This invention relates to the control of fuel injection from a fuel injection pump used for diesel engines or the like and, more particularly, to a system for controlling fuel injection with a solenoid valve provided on high and low pressure sides of the pump.
2. Related Art
In a well-known fuel injection device, a solenoid valve is provided in a fuel injection pump between the high pressure side thereof communicating with a compression chamber and the low pressure side leading to a fuel inlet. In the intake stroke, the high and low pressure sides are communicated to introduce fuel into the compression chamber from the low pressure side. In the compression stroke, the high and low pressure sides are blocked from each other for fuel injection. The end of the fuel injection is determined by adjusting the timing of causing the escape of high pressure fuel from the high pressure side to the low pressure side, i.e. the timing of the opening the solenoid valve.
In a fuel injection controller of this type, which was developed by the applicant, an armature is connected to a valve body of a solenoid valve, a spill chamber for causing the spill of high pressure fuel is formed around a head of the valve body, and an armature chamber accommodating the armature is formed around the armature. Further, a communication path communicating the spill and armature chambers is formed inside or around the valve body for pressure balance between the two chambers.
However, the fuel which is spilt from the high pressure side at the end of the fuel injection is under a very high pressure, typically 1,500 kg/cm.sup.2 and it was found that with the momentary fuel spill to the low pressure side caused with the opening of the solenoid valve a spike-like high frequency pressure wave, as shown by solid line in FIG. 3, is propagated from the spill chamber through the communication path to the armature chamber. The high pressure wave is propagated around the armature to strike the solenoid stator or the like. This is liable to result in deformation and corrosion of the solenoid surface over a long period of use.
To reduce damage due to this high pressure wave, it is thought to mount a thin metal sheet on the stator surface facing the armature. Doing so, however, undesirably reduces the electromagnetic force.
Besides, as shown in the solid line in FIG. 3, the armature chamber pressure is very low preceding the high pressure wave; actually it is presumed to be negative. This very low pressure causes a delay in the operation of opening the solenoid valve and has adverse effects on the fuel injection cut required for the fuel injection pump, that is, the rapid spill performance thereof.